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May 19, 1931. E. L. WIEGAND ELECTRIC HEATING APPARATUS Filed April 11, 1929 Edwig L Wiegagd L raaveaa'boac" 3 W gtfiozggga Patented May 19, 1931 UNITED STATES PATENT OFFICE EDWIN L. WIEGAND, OI PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO EDWIN L.

WIEGAND COMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION SYLVANIA ELEUIRIC HEATING APPARATUS Application filed April 11,

This invention relates to electric heating apparatus of the metallic resistor type and has for its object the provision of an assemblage of this nature having peculiarly high attributes of reliability and longevity.

In my Patents No. 1,614,330 and 1,614,331 granted January 11, 1927, I illustrated and claimed numerous electric resistance heating elements consisting of resistor wires submerged in electrically-non-conducting material and wholly surrounded by metal sheathing of diflerent shapes so as to be protected from injury by handling or by the absorption of grease and other cooking-liquids. I have found, however, by experience, that in some cases such a completely sheathed unit exhibits a 'eculiar phenomenon, especially when the o ject to beheated has a highcoeflicient of reflection or re-radiation. For example a bright aluminum vessel, while an excellent conductor after the heat has been absorbed by it, is a very poor receiver of heat by radiation; and its reception by metallic conduction, even though a good nominal contact may exist when the device is new, always decreases with age as the contact itself deteriorates, after which the heat must be transmitted more by radiation. Sometimes, in applications where the energy density is rather high, the reflection of heat from the surface even of a comparatively cool vessel is so great as to force the temperature of an interposedmetallic sheath to such a point as seriously to injure the sheathing metal, thus further impeding heat transfer and leading eventually to a breaking down of the unit itself.

A high rate of re-radiation may have much the same efiect even though the coefficient of'absorption be high. For example vessels or melting pots which themselves operate at a high temperature are diiiicult to heat by radiation from a metal surface, althou h in these the surface is generally a better a sorber. than bright aluminum; however, as the temperature rises the re-radiation also increases, so that the only value available for heat-transmission is the difference of temperature between the heating element. and the vessel heated which forces 1929. Serial No. 354,283,

up the temperature of the heating element in the same way as does a polished aluminum vessel at a lower temperature. Thus in the case of the high-temperature melting pot, for example, the resistance of the vessel to receiving heat is to force the heating'clement to high temperature and if sheathing is interposed between the refractory unit and the articles to be heated, that sheathing unless made of the more expensive high heat resisting alloys, is liable to progressive destruction, and the contact to steady deterioration.

Accordingly the object of the present invention is the provision of a new and improved assemblage and relation of heatingelement and heated-element which shall secure the advantages of the fully sheathed units without the disadvantages; the provision with a vessel or element to be heated of a partially-sheathed element so arranged as to be protected against injury or contamination without itself becoming disintegrated by the thermal results of the operation; the

rovision of a combination of heating and iieatedelements which shall secure new advantages of quick heating; while further results and advantages of the operation will become apparent as the description proceeds. The heating element shown herein is specifi cally claimed in my application Serial Number 297,612, filed August 6, 1928.

In the drawings accompanying and forming a part of this application I have shown certain typical embodiments of my inventive idea though without intent to limit myself to those embodiments which are chosen merely as being illustrative of the principles of my invention and not as being exhaustive of its details. Fig. 1 is a vertical sectional view through part of a liquid heater containing my improvements and Fig. 2 is a horizontal sectional view corresponding to the line 22 thereof, Fig. 3 is a vertical sectional view through the bottom part of a metal meltingpot and Fig. 4 a horizontal sectional view corresponding to the line Ir-4: thereof; Fig. 5 is a vertical sectional view through the bottom part of a percolator embodying my improvements, and Fig. 6 is a horizontal sectional view corresponding to the line 66 a 55 pt thereof; and Fig. 7 is a perspective v1ew of oneof m improved elements removed with parts bro en away to show the inter or construction. r In choosing liquid heaters or metal melters as illustrative embodiments of my invention I do not disclaim its use for heatin other types of devices. The heated device in F g. 1 consists of a sheet-metal vessel 10 havmg its bottom wall 11 slightly embossed upwardly as shown at 12 for the reception of the upper part of the heating element; and sa1d heat in element comprises a ribbon or w1 re 13 of i h temperatureand oxidation-resistmg metaIsubmerged in a closely-compacted mass 14 of electrically-insulating material leaving as high a heat-conductivity as may be, the whole embraced on the bottom and sides by a metallic housing 15. Without in any wlse limiting myself thereto, I have had my best success with certain of the more refractory oxide, aluminum oxide in the form of'corundum or granular zirconium silicate or a mixture of them being very satisfactory when mixed with just enough clay to constitute a binder without unduly lower1n g the meltin point or impairing the di-electnc strength 0 I the material. However, practically all the insulating materials which exhibit prolonged usefulness are of a somewhat porous and brittle nature and uire an intimate support, added to which 1t is desirable, in order to secure quick heating and diminish residual heat, to make such a heating-element much thinner and li hter than wou d be possible in case it were omogeneous in composition. J Hence, in order .to secure these advantages of lightness and protection I construct the unit with a fiat circular sheet of metal having itsedges rolled, s un or ressed u wardly to form a side we 16, an also pre erably a lip flange 17 defining the space in whic the lnsulating material 14 is compacted about the resistor 13. This element is then located-with its naked face closely presented to the bottom 11 of the vessel 10. The embosing 12 is not strictly necessary but is desirable for several reasons, among which are the fact that such a boss generally retains it sha e with a, minimum of tendency to warp; 0 that it helps establish the position of the heating element; also that it tends to assist in protecting the same grmst ingress of liquid; and there may be or reasons I The element'is clamped tightly against the bottom of the vessel in any suitable manner, here b means of the circular plate 18 'ppe tightl against the bottom 11 by a ad 19 rolle over the outwardly-projectmg1 edges of the two, and having at its center a ownwardly pressed boss 20 coo rating with the boss 12 to rovide a recess in which the element is tightly received. In this case I the head 19 is integral with a bottom memner ends are attached to terminals 25 projecting through thebottom 15 of the sheath and suitably insulated therefrom by washers 26.. I deem it unnecessary to illustrate the attachmentof these terminals to the resistor."

wire since this will be a 'parent to those skilled in the art. The em ossed portion of the plate 18 is apertured as shown at 27 for 9 these terminals, andin case the device is in-. tended for domestic use, the hollow bottom is preferably traversed by a metallic plate 28 and an asbestos sheet 29 laid thereon in order to prevent the heat of the element from injurmg the supporting surface. I have shown the sheet 28 as held in place by fibre feet 30 which further protectany article on which the device is set.

The receptacle 31 shown in Fig. 3 is made of a thicker wall, as for example cast iron, and against'the bottom of said'vessel is clamped a naked-top d, electric-resistance heating element of t e same kind of construction as shown in Fig. 1. v I have shown the base 32 also as made of cast metal, the abutting faces of the two parts being formed as before with a suitable recess 33 for. the tight reception and secure protection of the heating element. I have also retained the metal plate 28 and insulating layer 29 since these are desirable in all cases although they should alwa s be spaced from the heated element in or er to permit exchange of heat between difierent pgrtions'thereo and thus decrease the danger 0 essential characteristics of a percolator.

This percolator comprisesa receptacle 35 of any suitable shape having a bottom 36 preferably embossed upwardly to define the circular cylindrical wall 37 to which the false-bottom or funnel 38 carrying the geyser-tube 39 can be removably applied. A

heating element of the' type described and having a naked upper face is located in this recess and clamped against the bottom ,36 of attaining destructivetemperatures localthe receptacle in any suitable or desired man- 7 net. I

Having thus described my invention I claim 1s:

1. Electrically heated apgaratus comprising an element to' be heate an electric re-.

sistance heating unit comprising an electric resistance wire submerged in a mass of commoans pacted electrically insulatin material, s'aid mass having one face nake and' the other face covered by a metallic reinforcement, 21. second element adjacent to said first element, said first element and second element defining between them a substantially closed recess and said resistance unit located in said recess with its naked face presented to said first element and said metallic reinforcement presented to said secondelement.

2. Electrically heated apparatus comprising an article to be heated whose surface exhibits during heating a degree of counterradiation, an electric resistance heating unit comprising an electric resistance wire submerged in a. c ompacted mass of electrically insulating material, a metal reinforcing plate on the side away from said article, the face of the insulating material being naked on the side presented toward said article, and means additional to and separate from said reinforcing plate to hold said insulating ma terial in contact with the article to be heated and to return to said article any heat which escapes from said reinforcing plate.

In testimony whereof I hereunto aflix my signature.

EDWIN L. WIEGAND. 

